A. Field of Invention
The present invention relates generally to valve actuating devices and more particularly to a new and improved high speed solenoid valve actuator for an axial flow, fluid control valve.
B. Description of Related Art
A number of solenoid actuated fluid control valves currently exist commonly using the armature of a solenoid to act as a working component of the valve. According to the common structure of such actuators, the speed of operation of the valve is directly dependent upon the ratio of the axial force generated by excitation of the solenoid to the mass of the armature and/or any attachments thereto, everything else being equal. In a plunger type fluid control valve, the armature itself may comprise a plunger sliding within a portion of a solenoid bore around which a wire coil is wound, and a magnetic circuit is formed by the plunger, a pole piece, and the solenoid housing that extends from the pole piece, around the coil, and returns to the plunger. In such configuration, the axial force on the plunger is derived entirely from a first air gap between the opposing surfaces of the plunger and a solenoid pole piece wherein the lines of magnetic flux are generally parallel to the axis of the plunger. A second air gap also exists, consisting of the opposing surfaces of the housing and the plunger at the radial clearance at the opening where the plunger enters the solenoid bore. The second air gap therefore usually only exerts a radial force on the plunger and not an axial force. Thus the axial force to armature mass ratio does not increase as a result of the second air gap. Moreover, the second air gap decreases the speed of valve operation and increases the wear on the plunger by creating a frictional drag between the surfaces of the second air gap. Since the plunger is rarely, if ever, perfectly balanced and since the electromagnetic force across each air gap increases in inverse relation to the square of the air gap distance, there ia a tendency to close the air gap on one side only. When the plunger begins to tilt a very small amount, the radial gap proceeds to close at the nearest point, causing wear and tear on the contact points as well as friction drag slowing the speed of the armature.
An example of such a valve actuator device appears in U.S. Pat. No. 4826130 to Griffith which discloses the use of a polymeric film lubricant coating the parts that comprise the second radial magnetic air gap to reduce the detrimental effects of friction in that area. Another modification to increase the axial force is to enlarge the surface area of the axial air gap as is shown in U.S. Pat. No. 4658231 to Schwenzer. The Schwenzer actuator does not make any attempt to change the second air gap nor to reduce the mass of the armature, but merely seeks to ameliorate the negative effects of the radial orientation. Another adaptation designed to improve responsiveness is the polarized electro magnet disclosed in U.S. Pat. No. 4855,701 to Yokoyama similarly does not teach or attempt to axially align both air gaps. Still another modification of electromagnets appears as the stepped exterior armature of the electro magnetic device disclosed in U.S. Pat. No. 4553121 to Logie which provides multiple axial air gaps without attempting to axially align the radial air gaps of each coil, but rather achieving the results from a multiple coil configuration.
U.S. Pat. No. 4810,985 to Mesenich discloses a device which by utilizing a cup shaped external armature does align the second air gap in an axial direction. In particular, the valve shown as FIG. 5 in Mesenich appears to provide an solenoid axial flow valve wherein both air gaps are essentially axially oriented. The Mesenich valve is designed for fuel injection automobile usage and in order to provide axial flow without creating a radial air gap in the disclosed configuration, the coil is relatively short and large in diameter. The cup shaped armature extends from an annular central air gap, radially outward and around the coil exterior to a second annular air gap and with the attached valving apparatus comprises a significant mass. In addition, the armature has large surfaces that slide past opposing surfaces of both the stator and valve body, creating the likelihood of frictional drag, increasing wear and decreasing speed of operation. The cup shaped armature additionally displaces a large volume of fluid media upon actuation which would tend to slow the valve speed. The foregoing features of the Mesenich device appear to require opposing springs and a relatively large coil to maintain a high speed operation in a bulky design.
Particularly in the field of ink jet printing, it is frequently desirable to electrically control operation of multiple valve banks wherein radial compactness is a primary design priority as is speed of operation particularly the cycle from closed to open and back to closed position which determines the accuracy of the printing accomplished and is desirably in the 1600 Hertz range. Manufacturing economy is also an important consideration due to the number of individual valves utilized in each printing device. Since the diameter of such a valve is approximately 1/4 of an inch, the relatively complicated and bulky valves and actuators identified above are either impossible or difficult and uneconomical to manufacture and operate. In particular, the cup shaped armature of Mesenich does not appear to have the potential for sufficient reduction in diameter to be useful in ink-jet printing applications.
Inclusion of the above-identified previously issued U.S. Patents is intended for illustration of other known valve actuator devices and is not intended as a representation that the identified patents constitute relevant prior art nor that all such devices or patents are included, nor that the devices would be suggested for use in the field of ink-jet printing.